
//反转一个单链表。 
//
// 示例: 
//
// 输入: 1->2->3->4->5->NULL
//输出: 5->4->3->2->1->NULL 
//
// 进阶: 
//你可以迭代或递归地反转链表。你能否用两种方法解决这道题？ 
// Related Topics 链表 
// 👍 1691 👎 0

package leetcode.editor.cn;

/**
 * @Author:xpengfei
 * @Date: 2021-04-16 22:29:26
 * @Description：反转链表
 */
public class Ques206ReverseLinkedList {
    public static void main(String[] args) {
        Solution solution = new Ques206ReverseLinkedList().new Solution();
    }

    //Definition for singly-linked list.
    public class ListNode {
        int val;
        ListNode next;

        ListNode() {
        }

        ListNode(int val) {
            this.val = val;
        }

        ListNode(int val, ListNode next) {
            this.val = val;
            this.next = next;
        }
    }
    //leetcode submit region begin(Prohibit modification and deletion)


    class Solution {
        public ListNode reverseList(ListNode head) {
            // 迭代解法版本
            // 前一个节点
            ListNode prev = null;
            // 当前节点
            ListNode curr = head;
            while (curr != null) {
                // 当前节点的下一个节点
                ListNode nextNode = curr.next;
                // 当前节点指向前一个节点
                curr.next = prev;
                prev = curr;
                curr = nextNode;
            }
            return prev;
        }
    }
//leetcode submit region end(Prohibit modification and deletion)

}